1. Field of the Invention
This invention relates to a home base modem system in a wireless communication system that provides telephone, data and Internet connectivity to a plurality of users.
2. Description of Related Art
Several systems are currently in place for connecting computer users to one another and to the Internet. For example, many companies such as Cisco Systems, provide data routers that route data from personal computers and computer networks to the Internet along conventional twisted pair wires and fiber optic lines. These same systems are also used to connect separate offices together in a wide area data network.
However, these systems suffer significant disadvantages because of the time and expense required to lay high capacity communications cables between each office. This process is time consuming and expensive. What is needed in the art is a high capacity system that provides data links between offices, but does not require expensive communication cables to be installed.
Many types of current wireless communication systems facilitate two-way communication between a plurality of subscriber radio stations or subscriber units (either fixed or portable) and a fixed network infrastructure. Exemplary systems include mobile cellular telephone systems, personal communication systems (PCS), and cordless telephones. The objective of these wireless communication systems is to provide communication channels on demand between the subscriber units and the home base in order to connect the subscriber unit with the fixed network infrastructure (usually a wired-line system). Several types of multiple access systems currently exist for wirelessly transferring data between multiple sites. For example, wireless communication systems have typically used a Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA) type system to facilitate the exchange of information between two users. These access schemes are well known in the art.
Often in these wireless communication systems a modem is used for modulating and demodulating the information that is exchanged between users. Inside the modem circuit an equalizer is employed to correct distortions either in the wireless channel or fix imperfections in the analog circuitry. A novel equalizer with enhancements to improve performance especially using higher order QAM modulation is described herein.
In one embodiment, the method comprises demodulating a data stream transmitted between remote sites and a home base using stored parameters for each remote site comprising receiving data from a current remote site at a home base, retrieving a parameter associated with a next remote site from a memory, storing the retrieved parameter for the next remote site in a first buffer, storing a second parameter associated with the current remote site into the memory, determining the initial phase and gain values for the next remote site based on the retrieved parameter, receiving data from the next remote site at the home base, and demodulating the data received from the next remote site using the determined initial phase and gain values.
In one embodiment, the method comprises compensating for gain droop in a modem which stores equalizer coefficients across data bursts between a remote site and a home base comprising receiving channel data values from an equalizer, calculating the gain for the equalizer based on the received channel data values, and scaling the input to the equalizer to achieve a value of 1 based on the calculated gain.
In one embodiment, the method comprises minimizing errors caused by adapting equalizer coefficients for each data burst from a remote site to a home base comprising retrieving a first equalizer coefficient for a current remote site, demodulating a data burst from the current remote site, determining the S/N ratio for the received burst, determining the error rate from the demodulated burst, comparing the determined S/N ratio and error rate to defined thresholds, and updating the first equalizer coefficient based on the comparisons.
In one embodiment, the method comprises improving the convergence of an equalizer in a multi-modulation modem using a two part preamble comprising defining a first part of a preamble with a lower order section, wherein the lower order section is transmitted using QPSK modulation, defining a second part of the preamble with a higher order section, wherein the higher order section is transmitted using QAM 64 modulation, transmitting both the first and second parts of the preamble, receiving the transmitted preamble, and converging the equalizer based on the received preamble.
In one embodiment, the method comprises providing a soft reset to a modem comprising generating an interrupt to the modem, halting the modem interface, setting a reset bit, flushing a buffer, realigning the buffer, reprogramming the buffer, and restarting the interface.
In one embodiment, the method comprises determining an adaptation factor for an equalizer based on the expected modulation type of an incoming burst transmission comprising calculating channel characteristics and metrics for a first burst transmission from a remote site, comparing the channel characteristics and metrics, determining an expected modulation type for a second burst transmission from the remote site based on the comparison, selecting an adaptation factor based on the expected modulation type, and applying the selected adaptation factor to the second burst transmission.
In one embodiment, the method comprises correcting the phase shift caused by the storage of tap values after each incoming burst transmission comprising determining an angle of correction based on correlating the input and output of the equalizer and applying the determined angle of correction to the incoming signal.